Remove DImode expansions for 1-bit shifts

A left shift of 1 can always be done using an add, so slightly adjust rtx
cost for DImode left shift by 1 so that adddi3 is preferred in all cases,
and the arm_ashldi3_1bit is redundant.

DImode right shifts of 1 are rarely used (6 in total in the GCC binary),
so there is little benefit of the arm_ashrdi3_1bit and arm_lshrdi3_1bit
patterns.  The generated code is better and faster without these shifts
as it allows early expansion, optimization and better register allocation.

    gcc/
	* config/arm/arm.md (ashldi3): Remove shift by 1 expansion.
	(arm_ashldi3_1bit): Remove pattern.
	(ashrdi3): Remove shift by 1 expansion.
	(arm_ashrdi3_1bit): Remove pattern.
	(lshrdi3): Remove shift by 1 expansion.
	(arm_lshrdi3_1bit): Remove pattern.
	* config/arm/arm.c (arm_rtx_costs_internal): Slightly increase
	cost of ashldi3 by 1.
	* config/arm/neon.md (ashldi3_neon): Remove shift by 1 expansion.
	(<shift>di3_neon): Likewise.

From-SVN: r254237

4 files changed, 21 insertions, 67 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bfd68e9..a32a5ce 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,16 @@
+2017-10-30  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* config/arm/arm.md (ashldi3): Remove shift by 1 expansion.
+	(arm_ashldi3_1bit): Remove pattern.
+	(ashrdi3): Remove shift by 1 expansion.
+	(arm_ashrdi3_1bit): Remove pattern.
+	(lshrdi3): Remove shift by 1 expansion.
+	(arm_lshrdi3_1bit): Remove pattern.
+	* config/arm/arm.c (arm_rtx_costs_internal): Slightly increase
+	cost of ashldi3 by 1.
+	* config/arm/neon.md (ashldi3_neon): Remove shift by 1 expansion.
+	(<shift>di3_neon): Likewise.
+
 2017-10-30  Dominik Infuehr  <dominik.infuehr@theobroma-systems.com>
 
 	* config/aarch64/aarch64-simd.md (*aarch64_simd_mov): Rename
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 22e1693..813d29af 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -9430,6 +9430,9 @@ arm_rtx_costs_internal (rtx x, enum rtx_code code, enum rtx_code outer_code,
 		   + rtx_cost (XEXP (x, 0), mode, code, 0, speed_p));
 	  if (speed_p)
 	    *cost += 2 * extra_cost->alu.shift;
+	  /* Slightly disparage left shift by 1 at so we prefer adddi3.  */
+	  if (code == ASHIFT && XEXP (x, 1) == CONST1_RTX (SImode))
+	    *cost += 1;
 	  return true;
 	}
       else if (mode == SImode)
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index f241f9d..ddb9d8f 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -4059,12 +4059,6 @@
     {
       rtx scratch1, scratch2;
 
-      if (operands[2] == CONST1_RTX (SImode))
-        {
-          emit_insn (gen_arm_ashldi3_1bit (operands[0], operands[1]));
-          DONE;
-        }
-
       /* Ideally we should use iwmmxt here if we could know that operands[1]
          ends up already living in an iwmmxt register. Otherwise it's
          cheaper to have the alternate code being generated than moving
@@ -4081,18 +4075,6 @@
   "
 )
 
-(define_insn "arm_ashldi3_1bit"
-  [(set (match_operand:DI            0 "s_register_operand" "=r,&r")
-        (ashift:DI (match_operand:DI 1 "s_register_operand" "0,r")
-                   (const_int 1)))
-   (clobber (reg:CC CC_REGNUM))]
-  "TARGET_32BIT"
-  "movs\\t%Q0, %Q1, asl #1\;adc\\t%R0, %R1, %R1"
-  [(set_attr "conds" "clob")
-   (set_attr "length" "8")
-   (set_attr "type" "multiple")]
-)
-
 (define_expand "ashlsi3"
   [(set (match_operand:SI            0 "s_register_operand" "")
 	(ashift:SI (match_operand:SI 1 "s_register_operand" "")
@@ -4128,12 +4110,6 @@
     {
       rtx scratch1, scratch2;
 
-      if (operands[2] == CONST1_RTX (SImode))
-        {
-          emit_insn (gen_arm_ashrdi3_1bit (operands[0], operands[1]));
-          DONE;
-        }
-
       /* Ideally we should use iwmmxt here if we could know that operands[1]
          ends up already living in an iwmmxt register. Otherwise it's
          cheaper to have the alternate code being generated than moving
@@ -4150,18 +4126,6 @@
   "
 )
 
-(define_insn "arm_ashrdi3_1bit"
-  [(set (match_operand:DI              0 "s_register_operand" "=r,&r")
-        (ashiftrt:DI (match_operand:DI 1 "s_register_operand" "0,r")
-                     (const_int 1)))
-   (clobber (reg:CC CC_REGNUM))]
-  "TARGET_32BIT"
-  "movs\\t%R0, %R1, asr #1\;mov\\t%Q0, %Q1, rrx"
-  [(set_attr "conds" "clob")
-   (set_attr "length" "8")
-   (set_attr "type" "multiple")]
-)
-
 (define_expand "ashrsi3"
   [(set (match_operand:SI              0 "s_register_operand" "")
 	(ashiftrt:SI (match_operand:SI 1 "s_register_operand" "")
@@ -4194,12 +4158,6 @@
     {
       rtx scratch1, scratch2;
 
-      if (operands[2] == CONST1_RTX (SImode))
-        {
-          emit_insn (gen_arm_lshrdi3_1bit (operands[0], operands[1]));
-          DONE;
-        }
-
       /* Ideally we should use iwmmxt here if we could know that operands[1]
          ends up already living in an iwmmxt register. Otherwise it's
          cheaper to have the alternate code being generated than moving
@@ -4216,18 +4174,6 @@
   "
 )
 
-(define_insn "arm_lshrdi3_1bit"
-  [(set (match_operand:DI              0 "s_register_operand" "=r,&r")
-        (lshiftrt:DI (match_operand:DI 1 "s_register_operand" "0,r")
-                     (const_int 1)))
-   (clobber (reg:CC CC_REGNUM))]
-  "TARGET_32BIT"
-  "movs\\t%R0, %R1, lsr #1\;mov\\t%Q0, %Q1, rrx"
-  [(set_attr "conds" "clob")
-   (set_attr "length" "8")
-   (set_attr "type" "multiple")]
-)
-
 (define_expand "lshrsi3"
   [(set (match_operand:SI              0 "s_register_operand" "")
 	(lshiftrt:SI (match_operand:SI 1 "s_register_operand" "")
diff --git a/gcc/config/arm/neon.md b/gcc/config/arm/neon.md
index e715a5c..4452778 100644
--- a/gcc/config/arm/neon.md
+++ b/gcc/config/arm/neon.md
@@ -1221,12 +1221,8 @@
 	gcc_assert (!reg_overlap_mentioned_p (operands[0], operands[1])
 		    || REGNO (operands[0]) == REGNO (operands[1]));
 
-	if (operands[2] == CONST1_RTX (SImode))
-	  /* This clobbers CC.  */
-	  emit_insn (gen_arm_ashldi3_1bit (operands[0], operands[1]));
-	else
-	  arm_emit_coreregs_64bit_shift (ASHIFT, operands[0], operands[1],
-					 operands[2], operands[3], operands[4]);
+	arm_emit_coreregs_64bit_shift (ASHIFT, operands[0], operands[1],
+				       operands[2], operands[3], operands[4]);
       }
     DONE;
   }"
@@ -1325,13 +1321,9 @@
 	gcc_assert (!reg_overlap_mentioned_p (operands[0], operands[1])
 		    || REGNO (operands[0]) == REGNO (operands[1]));
 
-	if (operands[2] == CONST1_RTX (SImode))
-	  /* This clobbers CC.  */
-	  emit_insn (gen_arm_<shift>di3_1bit (operands[0], operands[1]));
-	else
-	  /* This clobbers CC (ASHIFTRT by register only).  */
-	  arm_emit_coreregs_64bit_shift (<CODE>, operands[0], operands[1],
-				 	 operands[2], operands[3], operands[4]);
+	/* This clobbers CC (ASHIFTRT by register only).  */
+	arm_emit_coreregs_64bit_shift (<CODE>, operands[0], operands[1],
+				       operands[2], operands[3], operands[4]);
       }
 
     DONE;